Method and means for activating cathodes



Jan.24,1933. 1,5595 1',s94,949

METHOD AND MEANS FOR ACTIYA'I'ING CATHODES -Fi1ed-Dec.' a, 1930 1 FIG; I

JNl ENTGR ya 551% v ATTORNEY Patented Jan. 24, 19 33 UNITED STATES PATENT OFF IlCE ESPE, 0F B E'BLIN-CHABLOTTENBUBG, GERMANY, ASSIGNOR T0 SIEMENS &

HALSKE AKTIENGESELLSCHAIT, OF SIEMENSSTAD'I NEAR BERLIN, GER/Mm, A

COMPANY OF GERMANY mn'mon AND ums ron Acrrvnrme cn'rnonns Application filed December 6, 1930, Serial No. 500,600, and in Germany March 18, 1980.

The activation. of el ctron emitting cathodes in discharge devices is easily accomplished at the present time with the aid of thermit reaction. The cathode of the evacuated vessel is heated and a potential applied between the cathode and anode, a suitable resistance being inserted in the circuit to prevent an excessive increase of the anode current. g small amount of a thermit mixture such for example, as aluminum and barium oxide is applied upon or in the anode. The anode is heated by means of a high frequency field to such a degree that the thermit reaction will be initiated. The temperatures necessary for the thermit reaction are rather high so that the anode must be heated to such an extent that there is danger of its meltmg or losing its shape. There is dangeralso that due to thehigh heating employed portions of the anode material may vaporize and deposlt upon cooler parts of the device, such for ex-,

ample, as the grid insulation or the press whereby the insulation between the electrodes may. be appreciably impaired and short circuits may result.

Such an intense heating of the anode would not of itself be necessary. It would only be necessary to heat the anode to a temperature which is just slightly above the ignition temperature of the thermit mixture. With eddy current heating, however, it is not possible -to .prevent the heating of certain portions more than others. It is well known, for example, that in the heating of a metal sheet.

that the edges become heated to a greater extent than the central portion of the sheet.

Similarly it happens that certain portions of the anode are heated excessively while other portions remain comparatively. cool. Those parts of the anode at which the thermit mixture is located and which require the greatest amount of heat will be raised to the necessary ignition temperature at thelast, while the .portions situated away from that on which the thermit mixture is located may already be heated to a considerably higher temperature.

According to the present invention the initiation of the thermit reaction is effected by forming microscopic places of high temperature by means of so-called scintillation or ignition points. It is not then necessary for the initiation of a thermit reaction that theentire thermit mixture be brought to the ignition temperature. It is suflicient that only a microscopically small part reach the critical temperature. The thermit reaction then automatically proceeds throughout the entire mass.

Electron bombardment may beused expediently forthe production of such scintillation or ignition points. If the proper precautions a're exercised so that the" cathode.

has a definite electron emission before it is activated by the thermit method, the cathode may be used to bombard the thermit mixture and to produce localized high temperatures at the scintillation or ignition points. The procedure for producing and activatmg a discharge device will be explained in the following specification with reference to the accompanying drawings. In Fig. 1 there is shown a discharge device 1 which contains an incandescent cathode 2, a grid .3, and an anode 4. The cathode 2 preferably consists of a core on which oxides, carbonates, hydrides, nitrites, separately or mixed, of alkaline earth metals, are applied. The grid 3 is connected with the cathode through a battery which represent or constitute the ignitioncenters. The electrons emitted from the cathode are drawn, under the influence of the a plied grid voltage, to the grid and strike t e grid with great speed. This electron bom- I bardment heats the grid and completely degasses it.

The cathode so treated shows certainemission qualities. Inasmuch as the metallic emission centers constitute only a limited portion of the cathode surface, the emission is not as great as it would be if the cathode surface were completely covered with an alkaline earth metal. 1

The electron emitting surface of the cathode may be increased by additional evaporation of alkaline earth metal. Here begins the second part of the activation process. Fig. 2 shows symbolically the circuit employed for the second part of the process. The numerals 1, 2, 3 and 4 designate the corresponding parts shown in Fig. 1. The grid and cathode are connected by a battery 5 and a protective resistance 6 so that the grid has a small positive potential with respect to the cathode. The cathode 2 is connectedwith the anode 4 through an anode battery 7, a stabilizing resistance 8 and a switch 9.

The electrons emitted from the cathode 2 are attracted to the highly positive anode through the influence of the slightly ositively biased grid and the influence o the iighly positive anode. The electrons not only come in contact with the anode material but also strike the surface of the thermit mixture which is so disposed that it can be struck by a large number of electrons.

The impin ing electrons produce a strong heating of t e thermit mlxture at microscopically small places and this heating is of sufiicient intensity to initiate the thermit reaction. During the thermit reaction metallic barium in the form of barium vapor entirelyor partially ionized by electron impacts is released. The positive alkaline earth metal ions pass to the negativecathode, combine with electrons on the cathode to become neutral alkaline earth metal atoms or molecules and therebycover the cathode with a layer of alkaline earth metal. The vaporized barium which does not deposit upon the cathode deposits upon other electrodes and operates as a getter material. It is, of course, obvious that any other getter material such, for example, as magnesium may also be employed in addition to the alkaline earth metals not deposited upon the cathode. Precaution must be taken, however, that these auxiliary getter materials do not deposit on the cathode and thereby seriously impair the electron emission properties of the cathode. The prime advantage of initiating the thermit 'reaction by the formation of scintillation or ignition points over the usual high frequency heating method resides in the fact that the temperature produced at the microscopically small points on the anode is approximately 200 lower than the temperature necessary for satisfactory high frequency heating, so that the previously mentioned disadvantages such as melting, distortion of the anode and the cathode, for the cathode temperature is I simultaneously increased by the ion-bombardment. This action occurs in a very short time and. a low volta e luminous arc is produced which may quic ly lead to the destruction of the entire discharge device or at least to the destruction of the activated cathode. The space between the anode and the cathode constitutes a negative resistance so that the discharge current increases while the voltage at the discharge space decreases. It is possible to utilize this phenomena to indicate the beginning of the low voltage luminous are.

ig. 3 shows in combination a discharge device 1 comprising a cathode 2, a grid 3, an anode et'and a grid battery 5, a protective resistance 6, an anode battery 7, a stabilizing resistance 8 and a switch 9. A voltage relay 10 is connected in arallel with the anode 4 and cathode 2 and unctions to indicate that the thermit reaction has taken place and a low voltage are discharge has formed.

Such indicating devices may seem to be superfluous inasmuch as the thermit reaction is indicated b a strong lighting in the discharge tube. owever, as the devices usually have highly mirrored glass walls, the illumination in the discharge device cannot always be seen with certainty so thatit is advisable that the presence of the illumination or the low voltage are be indicated b some signaling device as described. It is possible, of course, to use the voltage relay 10 to operate the switch 9 so that the activation process is automatically interrupted at the proper mo-' ment. It may be advantageous under certain conditions to allow the low voltage are discharge to continue for one or two moments before the discharge current is disconnected. For this purpose the voltage relay 10 may be provided with a retarding device which may give any desired retardation. The relay is preferably so constructed that the retardation period can be adjusted to any desired value. a

The invention is applicable not only to dischar e tubes having a grid but is equally applica le to discharge tubes having a plural- 1ty of grids or auxiliary electrodes.

What is claimed is:

1. In combination, an electron discharge device comprising a cathode, an anode adjacent said cathode, a thermit mixture including an alkaline earth metal com ound upon said anode, means for heating sai cathode, series means including a source of potential and a stabilizing resistance between said anode andsaid cathode, and indicating means in shunt with said series means.

2. In combination, an electron discharge device comprising a cathode, an anode adinsane j'acent said cathode, a. thermit mixture of an alkaline earth metal compound 11 on said anode, means for heatin said catho e means for applying a potentia betweensaid-anode and said cathode whereby said thermit mixture is ignited by electron bombardment, and means in shunt with said anode and cathode for indicating the voltage the-rebetween.

3. ln combination, an electron discharge l0 device comprising a cathode, an anode adjacent said cathode, and a thermit mixture in-' cluding an alkaline earth metal compound upon said anode, means for heating said cathode, a series circuit including a source 15 of potential between saidcathode and anode for causing ignition of said thermit mixture by electron bombardment, and means in shunt with said series circuit operable at a predetermined voltage between said anode 2 and cathode for opening said series circuit. a. In combination, an electron discharge device comprising a-cathode, an anode adjacent said cathode, a thermit mixture including an alkaline earth metal compound upon said anode, means for heating said cathode, series means between said anode and cathode including a source of potentialand a switch for causing ignition of said thermit mixture by electron bombardment, and means so in shunt with said series meansfor auto-V matically opening said switch whenthethermit reaction has occurred.

' 5. lln combination, an electron dischar e device comprising a cathode, an anode a jacent said cathode, a thermit mixture including an alkaline earth metal compound upon said anode, means for heating said cathode, a series circuit between said anode and cathode including a source of potential, 40 a stabilizing resistance and a switch, whereby said thermit mixture is ignited'by electron bombardment, and a relay in shunt with said series circuit for opening said switch to dis connect said source of potential when the thermit action has occurred.

6. A combination in accordance with claim" 5 in which said relay is provided with a retarding device.

lln witness whereof, I hereuntosubscribe RNEB ESPE.

5 my name this 12th day ggovember. 1930. 

